Philippine President Rodrigo Duterte on Tuesday told human rights groups criticizing his deadly anti-drug war to "go to hell" after ordering police back to the frontlines of the crackdown.

Duterte had removed the police less than two months ago in response to rising opposition to the campaign. But his spokesman said he was now reinstating them because drug crimes had risen in their absence.

The president dismissed criticism over the thousands of people killed in the drug war as he said the Philippines had turned into a "narco-state".

"You can go to hell, all of you!" Duterte said in a speech, referring to human rights groups, Catholic bishops and priests who had urged an end to the killings.

"I do not want Filipinos to be turned into fools during my time. You can do that at any other time but not during my time, during my watch."

Presidential spokesman Harry Roque said Duterte signed an order Tuesday reinstating the police to the drug war because there had been a "public clamor" for their return.

"There has been a notable resurgence in illegal drug activities and crimes committed," Roque said as he read the order.

Duterte, 72, was elected last year on a promise to eradicate drugs from society by launching an unprecedented campaign in which up to 100,000 people would die.

Since he took office, police have reported killing about 4,000 people in the crackdown.

Another 2,290 have been murdered in drug-related crimes, while thousands of other deaths remain unsolved, according to government data.

Many Filipinos continue to support the crackdown and believe Duterte is making society safer.

But in October he announced that the Philippine Drug Enforcement Agency would replace the police in the drug war following mounting public opposition, including rare street protests that were triggered by officers allegedly murdering three teenagers.

Duterte said later he had removed police from the drug war "in deference" to critics, including rights campaigners, Catholic bishops and the European Union.

However Duterte also repeatedly said he believed the anti-drug agency, with only about 2,000 officers, would not be able to effectively prosecute the crackdown. The police force has about 165,000 officers.

The October suspension was the second time Duterte had hauled police off the drug war.

Duterte said at the time the police force was "corrupt to the core". But he reinstated the police in March without making major reforms to address the graft issue.